1. Field of the Invention
The invention relates to a foam that resists corrosion and that is useful for reinforcing structural members and the like.
2. Discussion of the Related Art
It is known that a number of industries, e.g., the automobile industry, require parts that are both strong and light-weight. One attempt to achieve this balance between strength and minimal weight provides for hollow metal parts. However, hollow metal parts are easily distorted. Accordingly, it is also known that the presence of structural foam in the cavities of the hollow parts can improve strength and stiffness of such parts.
Generally, such foams comprise a thermosettable resin such as an epoxy resin, a blowing agent and a filler such as hollow glass microspheres. Preferably, these foams have a density of about 20-40 lb/ft.sup.3 (about 0.30-0.65 g/cc) and are able to withstand heat in excess of 175.degree. C., most preferably in excess of 200.degree. C. Optional ingredients include curatives, processing aids, stabilizers, colorants, and UV absorbers.
Specific formulas for structural foam can vary widely. For example, U.S. Pat. No. 5,575,526 teaches several structural foams based on polyester and epoxy resins. U.S. Pat. No. 5,755,486 discloses thermally expandable resin-based materials containing, for example, epoxy resin, acrylonitrile-butadiene rubber, calcium carbonate, carbon black, fumed silica, glass spheres, curing agent, accelerator, and blowing agent. Structural reinforcement foams such as, e.g., TEROCORE.RTM. (a product of Henkel Surface Technologies) are now used in a variety of industries.
One characteristic of structural reinforcement foams is that they start as expandable resins that form gas pockets (cells) when cured. When exposed to ordinary environmental conditions, these cells can trap salt and water. Salt and water corrode the metal parts, which are commonly in contact with the foam, and the resulting metal oxide degrades the ability of the foam to adhere to the metal. Eventually, the foam is forced from the metal part, thereby weakening the part.